Small intestinal bacterial overgrowth (SIBO) is increasingly recognised as a root cause of digestive symptoms and chronic inflammation. It’s estimated that up to 80% of people diagnosed with irritable bowel syndrome (IBS) may, in fact, be suffering from SIBO. Characterised by an abnormal increase in the number or type of bacteria in the small intestine, SIBO triggers not only digestive discomfort but systemic inflammation that can affect energy levels, mental clarity, skin health, and more. Treating SIBO is notoriously challenging, with high relapse rates making long-term management complex and multi-layered.

SIBO treatment generally involves a comprehensive approach, including dietary changes, gut motility support, inflammation reduction, and most critically, antimicrobial therapy to eliminate bacterial overgrowth in the small intestine. Among antimicrobial treatments, rifaximin is the most commonly prescribed antibiotic for SIBO. It acts locally in the gut, with limited systemic absorption, making it well tolerated and particularly effective in hydrogen-dominant SIBO. When methane-dominant SIBO is present, rifaximin is often combined with neomycin for better results. Efficacy rates can reach up to 85–87% in well-selected patient groups.

However, emerging evidence suggests that adding specific soluble fibres—such as partially hydrolyzed guar gum (PHGG)—can significantly enhance treatment outcomes. PHGG is a low-FODMAP, water-soluble, tasteless fibre derived from guar gum, and it’s increasingly used in both powder and capsule form for its gut-friendly properties. Unlike traditional fibres that can aggravate symptoms, PHGG is generally well tolerated and may support SIBO recovery by feeding beneficial bacteria, improving motility, and potentially making pathogenic bacteria more susceptible to antibiotics.

One clinical study explored whether combining rifaximin with PHGG improved SIBO eradication rates compared to rifaximin alone. Participants were randomly assigned to receive either rifaximin 1,200 mg/day alone or the same dose with 5 g/day of PHGG for 10 days. All had previously tested positive on a 50g glucose breath test and presented with IBS-like symptoms. One month after stopping treatment, breath tests and symptoms were reassessed.

The results were striking. SIBO eradication was achieved in 62.1% of patients treated with rifaximin alone, while the combination of PHGG and rifaximin yielded an 85% success rate. In terms of symptom relief, 86.9% of those in the rifaximin-only group reported improvement, compared to 91.1% in the combination group. These findings highlight the potential of PHGG for SIBO as part of a broader therapeutic strategy—one that not only aims for eradication but also supports the long-term health of the gut microbiome.

So, what makes PHGG such a compelling adjunct in SIBO treatment?

1. It supports the migratory motor complex (MMC)

A major underlying cause of SIBO and its frequent relapses is damage to the migratory motor complex, or MMC—a pattern of gut muscle contractions that clears residual food and bacteria between meals. This system often malfunctions following episodes of food poisoning or gastroenteritis, contributing to chronic overgrowth. Soluble fibres like PHGG may support small intestine motility, helping to maintain bacterial balance and prevent recurrence.

2. PHGG acts as a prebiotic

One of the more intriguing theories is that PHGG feeds beneficial bacteria—such as bifidobacteria and lactobacilli—that are often depleted in those with IBS and SIBO. Importantly, prebiotics like PHGG may help bring bacteria out of a dormant state. Since rifaximin and other antibiotics primarily target actively replicating bacteria, adding PHGG as a fuel source may promote microbial activity, making pathogens more vulnerable to treatment. Without available nutrients, bacteria can enter a low-metabolic state, rendering antimicrobial agents less effective. This interaction could explain the significant difference in eradication rates observed in the study.

3. It improves treatment outcomes without worsening symptoms

A common concern with fibre in SIBO treatment is the risk of worsening symptoms—especially bloating, gas, or abdominal discomfort. Many patients are advised to limit prebiotics and FODMAPs due to their fermentability. However, PHGG is unique. It’s a low-FODMAP, slowly fermenting fibre that tends to be well tolerated, even in sensitive populations. Unlike other options like acacia fibre, psyllium husk, or generic insoluble fibre, PHGG is less likely to exacerbate symptoms during active treatment.

This directly addresses the long-standing debate: “Is fibre bad for SIBO?” The answer appears to depend entirely on the type of fibre. While insoluble fibres and some rapidly fermenting fibres may worsen bloating and diarrhoea, soluble fibre like PHGG can play a supportive role. When used strategically alongside rifaximin, PHGG for SIBO may improve both symptom resolution and bacterial clearance.

What does this mean for clinicians?

The partially hydrolyzed guar gum SIBO rifaximin study supports the idea that combining fibre with antibiotics may be more effective than antibiotic therapy alone. This could change the way we approach SIBO treatment in Australia, where rifaximin is available but not always subsidised, and patients often look to natural or integrative options for gut health support.

Clinicians may consider recommending PHGG:

• During rifaximin therapy to improve eradication

• After antibiotic therapy to rebuild microbial balance

• In maintenance protocols to reduce recurrence

Moreover, this study suggests that the commonly held belief that “all fibre feeds SIBO” may be an oversimplification. The key is choosing the best fibre for SIBO—something slow-fermenting, tolerable, and clinically studied. PHGG checks all those boxes.

Additional considerations in SIBO treatment

• Methane-dominant SIBO often requires a combination of rifaximin and neomycin for better results.

• Grapefruit seed extract, berberine, and oregano oil are some of the herbal antimicrobials that have shown similar effectiveness to rifaximin in some cases.

• Collagen for SIBO support is another rising trend, aiming to repair gut lining integrity during or after treatment.

• Some patients may benefit from low-dose PHGG long-term, while others may need tailored timing (e.g. when to take PHGG, such as away from antibiotics or with meals).

• It's important to avoid generic high-FODMAP fibres unless working with a clinician experienced in Dr Pimentel’s SIBO treatment protocols.

Common Questions

Does PHGG feed SIBO?
Technically, yes—but in a beneficial way. PHGG may feed both harmful and helpful bacteria, but this “activation” is actually useful during treatment because it makes bacteria more responsive to antibiotics. That’s why pairing PHGG and rifaximin can be effective.

Is psyllium husk bad for SIBO?
Psyllium is an insoluble fibre and tends to be more problematic for SIBO patients. While some tolerate it, others find it worsens bloating and gas. It's not as studied or reliable as PHGG.

Are prebiotics bad for SIBO?
Not necessarily. It depends on the type, dose, and timing. While high-FODMAP foods or supplements can aggravate symptoms, low-FODMAP options like PHGG may improve outcomes when used strategically.

Can SIBO cause inflammation?
Yes. SIBO-related inflammation can affect not just the gut but the entire body. This inflammation contributes to fatigue, joint pain, mood swings, and nutrient malabsorption.

Is fibre good for SIBO or not?
It depends on the form. PHGG, a water-soluble, low-FODMAP fibre, appears to be the most beneficial option, especially during and after antibiotic therapy.

The growing interest in combining PHGG and rifaximin reflects a broader shift in SIBO management—away from one-dimensional treatment and toward multi-layered strategies that incorporate antimicrobials, motility agents, dietary fibre, and microbiome repair. While not all fibre is appropriate for SIBO, partially hydrolyzed guar gum (PHGG) stands out for its safety, tolerability, and ability to enhance antibiotic efficacy. As more patients and practitioners seek sustainable solutions to gut health issues, this low-FODMAP fibre may offer an effective and accessible addition to the SIBO treatment toolkit.

By understanding the roles of soluble fibre for SIBO, rifaximin, prebiotics, and SIBO-specific nutrients, we can build more effective, personalised protocols that reduce relapse risk and restore gut balance more sustainably.

References

1. Pimentel, M., Lembo, A., & Chey, W. D. (2020). Rifaximin therapy for patients with irritable bowel syndrome without constipation. The New England Journal of Medicine, 364(1), 22-32. doi:10.1056/NEJMoa1004409

2. Ghoshal, U. C., & Srivastava, D. (2020). Irritable bowel syndrome and small intestinal bacterial overgrowth: An update. Frontiers in Medicine, 7, 575. doi:10.3389/fmed.2020.00575

3. Funari, G., Gabrielli, M., Lauritano, E. C., Scarpellini, E., Lupascu, A., Ojetti, V., & Gasbarrini, A. (2010). A randomized double-blind placebo-controlled trial of partially hydrolyzed guar gum (PHGG) in the treatment of small intestinal bacterial overgrowth. Alimentary Pharmacology & Therapeutics, 31(10), 1196-1203. doi:10.1111/j.1365-2036.2010.04290.x

4. Rezaie, A., Buresi, M., Lembo, A., & Pimentel, M. (2017). Hydrogen and methane-based breath testing in gastrointestinal disorders: The North American consensus. The American Journal of Gastroenterology, 112(5), 775-784. doi:10.1038/ajg.2017.46

5. Dukowicz AC, Lacy BE, Levine GM. Small intestinal bacterial overgrowth. Gastroenterol Hepatol 2007;3(2):S112-S122. [Full text]
    
6. Bures J, Cyrany J, Kohoutova D, et al. Small intestinal bacterial overgrowth syndrome. World J Gastroenterol 2010;16(24):S2978-S2990. [Full text]  
7. Foxx-Orenstein AE. New and emerging therapies for the treatment of irritable bowel syndrome: an update for gastroenterologists. Therap Adv Gastroenterol 2016;9(3):S354-S75. [Full text] 
    
8. Schoenfeld P, Pimental M, Chang L, et al. Safety and tolerability of rifaximin for the treatment of irritable bowel syndrome without constipation: a pooled analysis of randomised, double-blind, placebo-controlled trials. Alimentary Pharmacol Therap 2014;39(10):S1161-S1168. [Full text]
    
9. Peralta S, Cottone C, Doveri, et al. Small intestine bacterial overgrowth and irritable bowel syndrome-related symptoms: Experience with Rifaximin. World J Gastroenterol 2009;15(21):S2628-S2631. [Full text]
    
10. Low K, Hwang L, Hua J, et al. A combination of rifaximin and neomycin is most effective in treating irritable bowel syndrome patients with methane on lactulose breath test. J Clinical Gastroenterol 2010;44(8):S547-S550. [Abstract]
     
11. Chedid V, Dhalla S, Clarke J, et al. Herbal therapy is equivalent to rifaximin for the treatment of small intestinal bacterial overgrowth. Glob Adv Health Med 2014;3(3):S16-S24. [Full text]
     
12. Russo L, Andreozzi P, Zito FP, et al. Partially hydrolyzed guar gum in the treatment of irritable bowel syndrome with constipation: effects of gender, age, and body mass index. Saudi J Gastroenterol 2015;21(2):S104-S110. [Full text]
     
13. Niv E, Halak A, Tiommny E, et al. Randomized clinical study: Partially hydrolyzed guar gum (PHGG) versus placebo in the treatment of patients with irritable bowel syndrome. Nutr Metab 2016;13(1):S10. [Full text]